1. Field of the Invention
The present invention pertains to a patient interface device for use in a pressure support system that supplies a flow of gas to the airway of a patient, and, in particular, to a patient interface device that includes a dampening cushion, and to a pressure support system that employs such a patient interface device.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in the patient's esophagus. For example, it is known to deliver a flow of breathing gas to a patient using a technique known as non-invasive ventilation (NIV). It is also known to deliver to the patient continuous positive airway pressure (CPAP) or variable airway pressure, such as a bi-level pressure that varies with the patient's respiratory cycle, or an auto-titrating pressure that varies with the monitored condition of the patient.
Non-invasive ventilation and conventional pressure support therapies, such as those noted above, involve the placement of a patient interface device, which is typically a nasal or nasal/oral mask, on the face of a patient. The patient interface device facilitates the delivery of a flow of breathing gas from a pressure/flow generating device (e.g., a ventilator, pressure support device, etc.) to the airway of the patient. Typical pressure support therapies are prescribed to treat a medical disorder, such as sleep apnea syndrome, in particular, obstructive sleep apnea (OSA), chronic obstructive pulmonary disease (COPD), or congestive heart failure.
Many patient interface devices (i.e., masks) include a mask shell having a mask cushion or mask seal attached thereto. When the patient interface device is donned by the user, the mask cushion contacts the surface of the patient's face. The mask shell and mask cushion are usually held in place by a headgear that wraps around the head of a patient. A typical headgear includes flexible, adjustable straps that extend from the mask shell to attach the patient interface device to the patient. For example, it is known to maintain such a patient interface device on the face of a patient with a headgear having upper and lower straps, each having opposite ends threaded through connecting elements provided on the opposite sides and top of the mask shell. The patient interface device and headgear may be referred to as a patient interface assembly.
It is also known to provide forehead supports, cheek supports, and/or chin supports with patient interface devices to provide support mechanisms to support the patient interface device on the patient's face. Patient interface devices having forehead cushions, spacers, and/or supports are described in U.S. Pat. Nos. 4,907,584; 5,243,971; 5,517,986; 5,570,689; 6,119,693 and 6,357,441. An example of patient interface devices having cheek cushions, spacers, and/or supports are described in U.S. Pat. Nos. 4,915,105 and 6,119,694. An example of a patient interface device having a chin cushion, spacer, and/or support is described in published U.S. patent application Ser. No. 10/953,642 (publication No. US 2005/0072428).
Generally, patient interface devices are designed such that a seal is created and maintained between the mask cushion and the patient's face. More specifically, undue gas leaks around the periphery of the mask cushion must be avoided. With many existing patient interface devices, the mask cushion must be compressed against the patient's face to eliminate these undue gas leaks. However, the compression may cause the patient to experience discomfort. This discomfort may discourage the patient from wearing the patient interface device, thus defeating the purpose of the prescribed pressure support therapy. This is especially a problem when the patient interface device is worn by the patient for an extended period of time, for example, in providing CPAP to treat OSA.
In the instances where a forehead, cheek, and/or chin cushion is employed to lend added support to the patient interface device, the tightening of the headgear straps to effect compression of the mask cushion may also cause the forehead, cheek, and/or chin cushions to compress. As a result, the patient may experience further discomfort.
Many patient interface device designs attempt to balance the competing interests of patient comfort and leakage minimization. In addressing these interests, many designs have focused on the mask cushion. Early mask cushion designs were typically a flap of material or a balloon that contacted the face of the user. Further design developments include contouring the patient contacting portion of the mask cushion and/or making the mask cushion customizable to the surface or underlying tissues of the user. Still further mask cushions have employed multiple flaps so that the outermost flap provides a sealing function. See, e.g., U.S. Pat. No. 4,971,051 to Toffolon.
A need exists, however, for a patient interface device that improves upon existing devices. More specifically, a need exists for a patient interface device having an improved mask cushion that increases patient comfort while reducing undue gas leaks during delivery of a positive airway pressure or flow of gas to the airway of the user. A need also exists for improved forehead, cheek, and/or chin cushions associated with the patient interface device.